The intracellular second messenger cAMP or cGMP is broken down and deactivated by phosphodiesterase (PDE), which is classified into at least types I to VII. PDE is widely distributed in the tissue and organs of the body. Among these, type IV phosphodiesterase selectively breaks down cAMP and is found in the central tissue and in the heart, lungs, kidneys, and other organs and in the various hemocyte components etc. Further, it is known to be involved in the derivation of IL-1 and IL-6, TNF-.alpha., and other various cytokines.
Catechol type derivatives such as rolipram, known to be a selective inhibitor of type IV phosphodiesterase, quinazoline type derivatives such as nitraquazone, xanthine type derivatives such as theophylline and denbufylline, etc. are being used or developed as antidepressants, antiasthmatics, antiinflamatorics, etc. No drug has however yet been developed which solves the problems such as the selectivity with other isoenzymes and various side effects. There is no satisfactory medicine which has this enzyme inhibiting action as the main mechanism for achieving the medicinal effect.
On the other hand, as a compound having a naphthyridinone skeleton, for example, as a compound having a carbonyl group at the 2-position in the 1,8-naphthylidine skeleton, there are known those described in JP-A-55-164682, and as a compound having a carbonyl group at the 2-position and a PDE IV inhibiting action, there are known those described in WO-A-94-12499, WO-A-96-06843, etc.
Further, as a compound having a PDE IV inhibiting action and a carbonyl group at the 4-position in a 1,8-naphthyridine skeleton, WO-A-97-04775 describes one where the 1-position substituent group is an ethyl group. Further, as the method of synthesis described in this publication, the method shown in the following formula was used, based on the method of Kaminsky et al. (J. Med. Chem. 1968, 11, 160). However, the 1-position substituent group disclosed in this method is only an alkyl group. ##STR2##
In the above reaction process, it is only possible to use a substitution reaction using a highly reactive alkyl halide (A--CH.sub.2 --Y), and therefore, the substituent groups which can be introduced to the 1-position are limited.